Embedded systems can be used in a variety of applications, including providing monitoring, sensing, control, or security functions. Such embedded systems are generally tailored to specific applications, according to relatively severe constraints on size, power consumption, or environmental survivability.
In particular, one class of embedded system can include sensor nodes, such as for sensing or monitoring one or more physiologic parameters. A sensor node having wireless communication capability can be referred to as a Wireless Sensor Node (WSN). Similarly, a sensor node located on, nearby, or within a body of a subject can be referred to as a Body Area Sensor node (BASN) or Body Sensor node (BSN). Sensor nodes can provide significant benefit to care providers, such as enabling continuous monitoring, actuation, and logging of physiologic information, facilitating automated or remote follow-up, or providing one or more alerts in the presence of deteriorating physiologic status. The physiologic information obtained using the sensor node can be transferred to other systems, such as used to help diagnose, prevent, and respond to various illnesses such as diabetes, asthma, cardiac conditions, or other illnesses or conditions.
A sensor node can provide particular value to a subject or care giver if the sensor node includes certain features such as long-term monitoring capability or wearability, for example. A long lifetime for a sensor node without maintenance, replacement, or manual recharging becomes ever more important as health care costs escalate or as more care providers attempt to transition to remote patient follow-up and telemedicine. It is believed that generally-available sensor nodes are precluded from widespread adoption because of a lack of extended operational capability or wearability.
For example, sensor nodes including a large primary or rechargeable battery can be uncomfortable to wear, and a sensor node having a smaller battery is still undesirable because patients or other users may not comply with the required recharging or replacement interval. Similarly, sensor nodes requiring conductive data transfer interfaces are generally cumbersome, because the wearer or care giver must manually connect a communication interface cable to the node to transfer information to or from the node. Wireless communication circuitry may reduce or eliminate the need for such cumbersome wired interfaces. But, such wireless circuitry can consume substantial amounts of energy further taxing a limited energy budget or limiting operating life of generally-available sensor nodes.